In a process of manufacturing semiconductor devices, a method of dry-etching a silicon oxide film formed on a surface of a semiconductor wafer (hereinafter, simply referred to as a “wafer”) without using plasma, has been known. Such a dry-etching method includes modifying the silicon oxide film to produce a reaction product, and heating the reaction product to vaporize (or sublimate) the reaction product. The dry-etching method etches the silicon oxide film by sequentially performing the modification process and the heating process.
Specifically, the interior of a modification chamber where a wafer is received is first controlled to have a low pressure close to a vacuum state. Subsequently, for example, a mixture gas of a hydrogen fluoride gas (HF gas) and an ammonia gas (NH3 gas) is supplied into the chamber while adjusting the wafer to have a predetermined temperature, so that a silicon oxide film is modified into a reaction product. Thereafter, the wafer is transferred from the modification chamber to a heating chamber where the reaction product formed on the silicon oxide film is heated and sublimated. By doing this, the silicon oxide film is etched.
Once the silicon oxide film is modified (i.e., the generation of the reaction product) to a certain degree of depth starting at a surface of the silicon oxide film, a saturation point is deemed to have reached and the silicon oxide film is not modified any further. That is, there is a limit to an etching rate of the silicon oxide film which is to be etched by one cycle of the modification process and the heating process. Thus, in order to obtain a desired etching rate of the silicon oxide film, a sequence of the modification process and the heating process need to be performed for a plurality of times.
This also requires repeatedly transferring the wafer between the modification chamber and the heating chamber, thus reducing throughput due to the time spent in transferring the wafer.
In order to reduce the number of repetitions of the modification process and the heating process, there is a method of adjusting a heating temperature depending on the type of a silicon oxide film or adjusting a partial pressure of the hydrogen fluoride (HF) gas to be introduced into the modification chamber during the modification process.
However, such a method performs the modification process and the heating process using respective chambers, resulting in reduced throughput due to the time spent in transferring the wafer between the respective chambers.
In addition, if the sequence of the modification process and the heating process is performed using the same chamber, it takes a long time to adjust a temperature of the wafer due to a difference in processing temperature between the modification process and the heating process. This prolongs an overall time required for etching the silicon oxide film. In particular, the wafer which has undergone the heating process, has a high temperature (about 200 degrees C.). As such, when performing the modification process again after the heating process, it takes a long time to cool the highly heated wafer. This prolongs the time required for performing a subsequent modification process on the silicon oxide film, thus resulting in reduced throughput.